A lubricant vane pump is a volumetric pump. The lubricant vane pump is provided with a pump rotor body holding radially slidable vanes rotating inside a shiftable control ring. The slidable vanes, the rotor body, and the walls of the control ring define a plurality of rotating pumping chambers, rotating in a pumping cavity. The pumping cavity is separated into a charge zone with an inlet opening, a discharge zone with an outlet opening, and an intermediate zone between the charge zone and the discharge zone. The intermediate zone is, seen in the direction of rotation, arranged between the charge zone and the discharge zone. The pumping chambers rotate from the charge zone, through the intermediate zone, to the discharge zone inside the control ring. The control ring is radially shiftable for providing an adjustable eccentricity with respect to the static rotor axis. By varying of the eccentricity of the control ring, the control ring is moved between a high pumping volume position and a low pumping volume position, thereby adjusting the pump stroke.
The pump comprises a pretensioning element which pushes the control ring to a high pumping volume direction. The control chamber acts against the pretensioning element. If the rotational speed increases, the pressure in the control chamber rises, so that the control ring is pushed into a low pumping volume direction to keep the outlet pressure constant. If the rotation speed decreases, the outlet pressure decreases as well, so that the control ring is pushed into a high pumping volume direction, with the effect that the lubricant is still pressurized with a more or less constant level independent of the rotational speed of the pump rotor or of the engine.
The lubricant pumped by the lubricant vane pump is incompressible oil. In a cold start action, the state of the art pump control systems lack proper functionality so that the priming time can be too long with respect to the engines' demand. One reason therefor is that the lubricant cannot fill the spring chamber due to its low viscosity, so that the control ring is forced into the low volume direction. Present solutions use high stiffness pretensioning elements to force the control ring into the high volume direction with high forces. However, this solution deteriorates the control quality of the pump in its standard condition (i.e., high temperature performances).